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Photogrammetric processing of archival stereo imagery offers the opportunity to reconstruct glacier volume changes for regions where no such data exist, and to better constrain the contribution to sea-level rise from small glaciers and ice caps. The ability to derive digital elevation model (DEM) measurements of glacier volume from photogrammetry relies on good-quality, well-distributed ground reference data, which may be difficult to acquire. This study shows that ground-control points (GCPs) can be identified and extracted from point-cloud airborne lidar data and used to control photogrammetric glacier models. The technique is applied to midtre Lovénbreen, a small valley glacier in northwest Svalbard. We show that the amount of ground control measured and the elevation accuracy of GCP coordinates (based on known and theoretical error considerations) has a significant effect on photogrammetric model statistics, DEM accuracy and the subsequent geodetic measurement of glacier volume change. Models controlled with fewer than 20 lidar control points or GCPs from sub-optimal areas within the swath footprint overestimated volume change by 14–53% over a 2 year period. DEMs derived from models utilizing 20–25 or more GCPs, however, gave volume change estimates within ∼4% of those from repeat lidar data (−0.51 m a−1 between 2003 and 2005). Our results have important implications for the measurement of glacier volume change from archival stereo-imagery sources.

Based on a presentation given at the one-day symposium of the Remote Sensing and Photogrammetry Abstract Research has shown the importance of measuring topography for surface change detection and that the use of remote sensing methods is ideal for this application. A prerequisite for measuring change is a historical data-set that covers the time period of interest. Many remote methods of topographic data collection such as lidar are relatively recent developments and therefore cannot provide records longer than about a decade. Alternatively, aerial photography has been in common use since the early 20th century and archives upwards of 50 years are therefore not uncommon. While photogrammetry is dependent on well distributed, high quality ground control points (GCPs), such data has been successfully applied retroactively. Therefore, contemporary lidar data, which requires little ground-truth data, should be an ideal source of GCPs for controlling historical aerial photographs. This study aims to evaluate the success with which GCPs can be extracted from a highresolution lidar data-set for controlling aerial photography for digital elevation model (DEM) production. Using a data-set collected in Upper Wharfedale, northern England, GCPs were measured both by means of a lidar data-set and by using traditional field-based methods. The results showed that while the use of lidarderived ground control produced a DEM of inferior quality, increasing the number of GCPs used in the model produced results comparable to the GPS-controlled DEM. These results are significant especially for surface change detection research in remote areas where high quality ground control is difficult to secure.

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